The present invention generally concerns electrostatic recording systems, and more particularly it concerns a method and an apparatus for electrostatic recording by doubly controlling ion flows wherein the controlling voltage for recording is low (below 50 V), the electrostatic latent image recording unit can be placed at a distance (not less than 0.1 mm) away from the part where recording is to be made, and the high speed recording can be conducted.
In the prior art, there have been proposed various electrostatic recording methods: one example is disclosed in the Proceedings of the Fifth Conference of the Institute of Image Electronics Engineers of Japan, 1977, "Ion Flow controlled Electrostatic Facsimile Recording" by Kubota and Miyoshi, and it discusses a method of obtaining a desired pattern of electrostatic latent image by using control electrodes having apertures and controlling the ion flow which passes these apertures. More particularly, a corona charger, and a back electrode are opposed with a predetermined distance therebetween, control electrodes are provided between the two, and an electrostatic recording paper is fed in front of the back electrode. The control electrode is so constructed that paired conductive layers are opposed across the thickness of an insulator and an aperture is bored which passes through the conductive layers and the insulator. When the controlling voltage is applied across the paired conductive layers of such a control electrode in such a way that the electric field within the aperture is reverse to an electric field directed from the corona charger to the back electrode, the ion flow passing the aperture and bombarding the recording paper may be cut off by the electric field within the aperture. Thus, a pattern of electrostatic latent image may be formed on the electrostatic recording paper corresponding to the application of the control voltage. In this method, although the controlling voltage for recording is advantageously as low as several of tens of volts and the control electrode is spaced apart from the recording paper, leaving behind spacing of more than 1 mm, there arise problems that the recording speed is very low, 0.67 mm/sec. at the most, because of the low intensity of corona current, and that a special electrostatic recording paper having insulating layers on the surface must be used intead of plain papers.
Another example of using an electrode pin array for electrostatic latent image formation is disclosed in the Proceedings of 1977 IEEE-IAS Conference "High Speed Nonimpact Printer Using Dielectric Drum" by Horie and Takahashi. According to this example, a corona charger and a latent image forming electrode pin are arranged along the outer periphery of the insulator drum which is rotatably supported. After uniformly charging the insulator drum surface with the corona charger, the charge on the insulator drum is neutralized responsive to the recording signal supplied to the latent image forming pin electrode to obtain a pattern of electrostatic latent image.
Although a high speed recording is possible according to this method, there are such defects as a need to apply a high voltage pulse (several of hundreds of volts) to the latent image forming electrode pin, a need to control the space between the electrode pin and the insulator drum to 20-+um, and that the electrode pin will discharge owing to the high working voltage when contaminated, thereby making the record unstable.
Further in the art, there is known a method of controlling the ion flow without using the above-mentioned control electrode or the latent image forming electrode pin, but using a photoconductor mesh (a metal mesh which is deposited with a photoconductive layer in such a way as not to fill the mesh apertures). More particularly, the photoconductive layer on the photoconductor mesh is charged by the corona discharge from a corona charger provided on the side of the photoconductive layer, and the photoconductor mesh is then exposed to light from a light source provided on the side of the photoconductive layer according to a desired pattern to neutralize the photo-conductive layer thus exposed, thereby forming the pattern of electrostatic latent image. Finally, by discharging corona from a corona charger provided on the side of the metal mesh, a recording paper facing the photoconductive layer is charged. In the last step of the above-mentioned process, the area including the photoconductive layer neutralized by being exposed to the light permits corona ion to pass through the mesh apertures to charge the recording paper responsive thereto whereas within the area including the photoconductive layer which has not been exposed to the light and where the charges of the same polarity as that of the discharged corona remain, the corona ion cannot pass the mesh apertures and the portion corresponding thereto on the recording paper does not become charged, thereby forming the pattern of electrostatic latent image on the recording paper. Such a conventional example is disclosed in the Proceedings of the Society of Electrophotography of Japan, 1975, "Latent Image Formation Using Photoconductor Mesh", Ozeki et al. Subject matters of U.S. Pat. Nos. 3,625,604, No. 3,694,200, No. 4,006,983, and No. 4,064,439 are also based on the same principle as the above.
In this method, the photoconductive layer does not contact the recording paper and the recording speed is as high as 10 cm/sec. When applying to the printer, however, the optical scanning system is used for recording which requires a laser source, a modulator, and a lens system, complicating the construction and causing difficulties in adjustment. The use of photoconductive layer shortens the life of the photoconductor mesh.